Illustration of Galileo at Jupiter

Flight controllers at NASA's Jet Propulsion Laboratory are working to analyze a problem that occurred during the unfurling of the Galileo spacecraft's main communications antenna Thursday, April 11.

Commands to unfurl the 16-foot-diameter umbrella-like antenna were issued by Galileo's computers on schedule at about 12:50 p.m. Pacific Daylight Time on Thursday. The action was to be completed in less than 10 minutes.

Normally microswitches would open when the unfurling was completed, signaling that the operation was successful. Data received from Galileo, however, indicate that the switches did not open.

Data suggest that the antenna partially deployed, but did not open fully.

Members of the flight team will continue detailed analysis of data sent by Galileo during the deployment attempt before taking any further action on the spacecraft.

Project officials emphasized that the deployment problem poses no immediate problems for the spacecraft, which otherwise is functioning properly.

The antenna -- a modified version of the design used in NASA's Earth-orbiting Tracking & Data Relay Satellites -- has a surface made of gold-plated molybdenum wire woven into a mesh. The mesh is stretched across 18 graphite-epoxy ribs and connected with elastic epoxy bands.

The high-gain antenna, made of metal mesh, has been stowed behind a sun shield since Galileo's launch in October 1989, to avoid heat damage while the spacecraft flew closer to the sun than the orbit of Earth.

The antenna unfurling is driven by a set of redundant motors which turn a worm gear. This gear pushes levers which spread the antenna's ribs, much as an umbrella is opened.

The unfurling was expected to slow Galileo's spin rate, much as the spinning of an ice skater slows when the skater's arms are extended. Data showed that Galileo's spin rate in fact slowed, but not as much as expected for full deployment.

Unfurling of the antenna is necessary for Galileo to send scientific data to Earth at much higher rates over greater distances than it can with the low-gain antennas it has used since launch.

The Galileo Project is managed by the Jet Propulsion Laboratory for NASA's Office of Space Science and Applications.

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